Passenger train locomotives include a head end power module for generating power for auxiliary demands on the train such as lighting, a 120 V power supply, and other electric needs. The head end power module, usually at the front of the locomotive or “head” of the train, is often equipped with at least one internal combustion engine to drive one or more electric generators. Some head end power modules include one or more power inverters to invert varying input DC link voltage from the generator to a constant output AC voltage. In order to produce constant power to supply the auxiliary demands, the generator typically runs at a high RPM (usually top operational speed) at all times. When the train is stopped at a station, running the generator at top speed may be loud and may consume high amounts of fuel.
One example of a system for converting AC power is described in U.S. Pat. No. 7,385,372 (“the '372 patent”) filed by Ahmad on Jun. 10, 2008. The '372 patent describes a system that includes two inverters arranged in parallel to receive DC power from two rectifiers. The two inverters provide power to one or more traction motors and to auxiliary devices. By using two inverters, the generator may be run at low speeds.
Although the '372 patent may provide for reduced generator speeds, it may still be less than optimal. In particular, the system of the '372 patent may be difficult to control. In order to reduce the operational speed of the generator, the two power inverters must be configured in parallel. However, synchronization of the two power inverters may be sub-optimal at lower speeds because control of two inverters configured in parallel is difficult. In particular, the output of the two converters is difficult to synchronize when controlled together due to varying generator speeds in operation. Without synchronized independent control of the power inverters, an associated harmonic content may be unnecessarily high.
The head end power module of the present disclosure solves one or more of the problems set forth above and/or other problems in the art.